os.system() execute command under which li

问题:

I am using /bin/tcsh as my default shell.

However, the tcsh style command os.system('setenv VAR val') doesn't work for me. But os.system('export VAR=val') works.

So my question is how can I know the os.system() run command under which shell?

回答1:

os.system() just calls the system() system call ("man 3 system"). On most *nixes this means you get /bin/sh.

Note that export VAR=val is technically not standard syntax (though bash understands it, and I think ksh does too). It will not work on systems where /bin/sh is actually the Bourne shell. On those systems you need to export and set as separate commands. (This will work with bash too.)

回答2:

Was just reading Executing BASH from Python, then 17.1. subprocess — Subprocess management — Python v2.7.3 documentation, and I saw the executable argument; and it seems to work:

$ python
Python 2.7.1+ (r271:86832, Sep 27 2012, 21:16:52) 
[GCC 4.5.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> print os.popen("echo $0").read()
sh
>>> import subprocess
>>> print subprocess.call("echo $0", shell=True).read()
/bin/sh
>>> print subprocess.Popen("echo $0", stdout=subprocess.PIPE, shell=True).stdout.read()
/bin/sh
>>> print subprocess.Popen("echo $0", stdout=subprocess.PIPE, shell=True, executable="/bin/bash").stdout.read()
/bin/bash
>>> print subprocess.Popen("cat <(echo TEST)", stdout=subprocess.PIPE, shell=True).stdout.read()
/bin/sh: Syntax error: "(" unexpected
>>> print subprocess.Popen("cat <(echo TEST)", stdout=subprocess.PIPE, shell=True, executable="/bin/bash").stdout.read()
TEST

Hope this helps someone,
Cheers!

回答3:

These days you should be using the Subprocess module instead of os.system(). According to the documentation there, the default shell is /bin/sh. I believe that os.system() works the same way.

Edit: I should also mention that the subprocess module allows you to set the environment available to the executing process through the env parameter.

回答4:

If your command is a shell file, and the file is executable, and the file begins with "#!", you can pick your shell.

#!/bin/zsh
Do Some Stuff

You can write this file and then execute it with subprocess.Popen(filename,shell=True) and you'll be able to use any shell you want.

Also, be sure to read this about os.system and subprocess.Popen.